1. Field of the Invention
The present invention relates generally to wireless communication technology, and more particularly to an initial connection procedure between user equipment and network equipment in a wireless communication system.
2. Description of the Related Art
In wireless communication systems there is the need for a logical connection between a mobile station (also referred to as user equipment (UE), a user terminal, a mobile terminal, a wireless data terminal and a cellular phone) and radio access network. The radio access network may comprise one or more base stations (also referred to as a Node B, for example in 3GPP nomenclature) together with one or more radio network controllers (RNCs). The logical connection provides a context for a particular network to UE communication link over which data may be transferred without miscommunication of the data to network elements or UEs in the system that are not intended to take part in the communication.
In the radio access network system defined by 3GPP, the logical connection between the user terminal and the radio access network is defined by radio resource control (RRC) connection states. Two of the main RRC connection states are defined as RRC connected and RRC idle.
If there is a logical connection between the user terminal and the radio access network, then the user terminal is said to be in RRC connected state. The existence of a user terminal in RRC connected state can be determined within a cell or multiple cells. Therefore, the radio resources for a particular user terminal can be managed efficiently by the wireless network. In contrast to RRC connected state, a user terminal in RRC idle state has no logical connection to the wireless access network. Thus, the user terminal in RRC idle state can only be determined within the core network or area that is larger than the cell, such as a location area or routing area.
When the user terminal is initially switched on by the user, a public land mobile network (PLMN) is selected and the user terminal searches for a suitable cell to be camped on to and remains in RRC idle state in the corresponding cell. An initial RRC connection may be initiated either by the network or by the user equipment. For example, in the case of a UE initiated connection for a UE in the RRC idle state, the UE requires an initial connection to the network and sends a RRC connection request message to the network. By means of a further example, in the case of a network initiated connection, an RRC connection request message may also be sent by the UE in response to receipt of a paging message from the network (the network having sent the paging message to the UE to illicit the commencement of an RRC connection procedure).
There are thus a number of reasons for RRC connection request by the UE. For example: (1) Initial cell access: when the UE attempts to make a call, the UE needs to establish an RRC connection; (2) Paging response: when transmitting a response message to a paging message; (3) Cell update: when the UE selects a suitable cell while in idle mode; (4) UTRAN Routing Area (URA) update: when the UE selects a suitable URA while in idle mode; and (5) Multimedia Broadcast and Multicast (MBMS) connection: in order to receive MBMS service and request for MBMS point-to-point connection.
In the conventional RRC connection procedure, the user terminal initiates the connection procedure by transmitting a RRC connection request message to the network using common uplink transport channels. The common uplink transport channels are shared by a plurality of UEs and are used for non-scheduled data transmission.
The network considers the connection request and may return on downlink either an RRC connection setup message (in the event of a successful admission) or an RRC connection reject message (in the event of an unsuccessful admission). In both cases the message is sent using common downlink transport channels which are (similar to the uplink common channels) shared by a plurality of UEs and used for non-scheduled data transmission.
The common transport channel over which messages from the user terminal to the network are transmitted during this initial RRC connection phase are termed random access channels. Random access transmission may similarly be referred to as unscheduled transmissions, as no explicit scheduling or coordination of the transmissions is carried out. Due to this lack of explicit coordination, there exists a probability that one mobile will transmit using the same uplink transmission resources or uplink identity as another user. In this instance, the communication reliability of both transmissions may be compromised due to the mutual logical or actual interference the uplink messages generate at the receiving base station. These cases, in which more than one mobile transmits on a defined set of uplink resources, may be referred to as collisions.
A further description of collisions, unscheduled access and scheduled access may be found in U.S. patent application Ser. No. 11/263,044, filed on Oct. 31, 2005, titled “FREQUENCY DOMAIN UNSCHEDULED TRANSMISSION IN A TDD WIRELESS COMMUNICATIONS SYSTEM” to inventor Nicholas W. ANDERSON, and which is hereby incorporated by reference.
The common downlink transport channels used to convey the corresponding messages from the network to the user terminal are termed forward access channels (FACH).
System resources are typically reserved for these uplink and downlink common transport channels. The radio resources used for common channels are typically separated from the radio resources used for other transport channels. Examples of other types of transport channel comprise dedicated transport channels and shared transport channels. In the case of dedicated transport channels the data is mapped to a sub-set of the total radio resources assigned on a long term basis to a particular user or connection. Conversely, in the case of shared channels, the data for each user is more dynamically mapped to a part of a pool of radio resources assigned within the set of total radio resources under control of a resource scheduler located typically within the MAC layer (layer 2) of the network. The radio resource in this instance is thus shared amongst users and is arbitrated by the scheduler. This is to be contrasted against the case for common channels in which the users share the radio resource but in a non-scheduled manned.
The use of shared channels only can provide benefits in terms of system capacity when compared to the use of multiple channel types within the system (such as mixtures of common, shared and dedicated types) wherein each is assigned for a particular traffic type. This is because, by multiplexing all traffic types onto only shared channels, the scheduler can dynamically adapt the resources assigned to the varying instantaneous loads presented by each traffic type. In contrast, if for example we assign one traffic type exclusively to common channels and another traffic type exclusively to shared channels, then variations in the traffic loads offered by each traffic type cannot be accommodated without reconfiguring the respective portions of the total radio resource space assigned firstly to common and secondly to shared channels. This reconfiguration of radio resources is typically a slow process and the system is therefore unresponsive to fast variations in load. A consequence of this is that in current systems, the fraction of the total radio resource space assigned to common channels often has to be designed with a worst-case consideration in mind and radio resource usage efficiency is therefore suboptimum.
Following a conventional RRC connection establishment procedure, the existence of the UE is known by the network and a shared channel address or UE ID may then be assigned by the network only at the completion of the connection establishment procedure. Therefore, shared channels may only be used after the normal RRC connection procedure has been accomplished using the common channel procedures. A significant portion of the total radio resource space must therefore be pre-assigned to the common channels to carry the connection establishment traffic. The user terminal specific layer 2 connection context used for the shared channel operation can only be established at the completion of the RRC connection procedure.
In addition, known wireless communication systems expend a substantial amount of time and exchange a number of signaling messages on unshared and common channels to establish an initial layer 2 context for shared channel operations and this can contribute to communication delay. Furthermore, the existence of a plurality of channel types and associated protocols, procedures and attributes can significantly increase system implementation complexity.
For the above-mentioned reasons, an improvement to the initial system access and RRC connection procedure is desirable in order to improve radio resource usage efficiency, to reduce communication delay and to simplify system implementation complexity.